The present invention relates to a domestic appliance having at least one component which comprises a surface that can become laden with organic dirt, said surface comprising a photocatalyst and said surface being associated with a photoradiation source for irradiating the photocatalyst with an activating electromagnetic radiation.
A domestic appliance of this type is disclosed by each of the publications JP 11-123299 A, JP 11-137894 A and JP 11-137881 A. Accordingly, a washing solution container and, contained therein, a washing drum rotatable about a vertical axis and coated with layers of a photocatalyst are arranged in a washing machine, and a movable ultraviolet light source is provided by means of which the layers can be irradiated with ultraviolet light to activate the photocatalyst. Parts of the washing drum that could shade a layer of the photocatalyst from the photoradiation source can be made from material which is transparent to the radiation.
In a water-carrying domestic appliance, in general, objects that are soiled with different types of dirt are cleaned. Thus, in a dishwasher, food residues arise and the range of soiling of laundry items to be cleaned in a washing machine is usually greater. It is common to all water-carrying domestic appliances that soiling occurs therein, particularly at the less accessible sites, and can accumulate at such sites. Such soiling can be a good nutrient medium for microorganisms such as bacteria and fungi in a moist warm atmosphere prevailing in such a domestic appliance and can thereby cause additional soiling.
For example, in a laundry treatment device such as a washing machine, on frequent use of wash programs with cold washing solutions, in a long phase of inactivity with the door closed or under unfavorable siting conditions, bad odors and/or visible soiling can occur. A possibility for cleaning at such poorly accessible regions is therefore desirable. It is also desirable that preventative measures can be taken against microorganisms even where no externally perceptible effects occur. Overall, therefore, it is useful if such nuisance soiling can be prevented or, as far as possible, eliminated.
A variety of measures against such soiling are known from the prior art. In particular, sometimes, device cleaning programs are offered with which, at high temperatures and with the aid of washing agents and possibly with increased washing solution levels and/or at higher drum rotation speeds, i.e. with an increased input of mechanical energy, built-up dirt can be combated. Also known are the use of ozone and UV-C radiation to remove organic dirt. Also known are measures for killing microorganisms using Ag+ or Cu+ ions in a washing solution or on the surfaces of the materials in contact with the washing solution. Other methods aim at the thermal destruction of any microorganisms present by increasing the temperature at the surfaces of the components in contact with the washing solution by means of direct or indirect energy transfer (water, steam, microwaves). Also known from the aforementioned documents is the use of photocatalysts. A disadvantage of said known methods and measures is, for example, the high cost for equipment and/or operation thereof in order to achieve relevant effects. In the case of the use of Ag+ and Cu+ ions, disadvantageous effects involve the pollution of ground and waterways.
From the documents WO 2005/108505 A1, EP 1 205 244 A1 and EP 1 204 245 A1, minerals are known, the surfaces of which are able to activate oxygen molecules by irradiating them with visible or ultraviolet light such that the readiness thereof to undergo chemical reactions is significantly increased. This effect is commonly known by the designation “photocatalysis”. Each of said minerals is a semiconductor with a band gap which permits the creation of an electron-hole pair in said semiconductor by a quantum of visible or ultraviolet light. It is also to be assumed that a mineral of this type has an affinity for oxygen, which permits activation of the oxygen by transferring energy from the semiconductor. The known minerals include titanium dioxide, cadmium sulfide, tungsten trioxide and zinc oxide.
It is also known to alter a semiconductor of this type by doping or similar modification with elements such as carbon, boron, nitrogen, phosphorus, sulfur, chlorine, arsenic, selenium, bromine, antimony, tellurium and iodine such that the wavelength of light needed to evoke the photocatalysis is increased. Titanium dioxide is cited as an example: in order to evoke the photocatalysis with pure titanium dioxide, irradiation with ultraviolet light having a wavelength of between 380 nm and 400 nm corresponding to the UV-A range is required. According to the publication WO 2005/108505 A1, it is possible to generate a titanium dioxide modified with carbon and having the form of a powder at which photocatalysis occurs merely on irradiation with visible light. This powdered photocatalyst is usable in components made from concrete, ceramics, paper and woven fabrics in the building industry and the automotive industry, as well as in photovoltaic cells, air-conditioning units and apparatus for cleaning or sterilizing air or water.
Of the known materials which exhibit photocatalysis under corresponding conditions, titanium dioxide is particularly distinguished by being chemically largely inert and non-toxic, as well as being known in many uses, particularly as a white pigment and being produced and marketed on a large industrial scale.